Early clocks were not reliable enough at sea, so on-board ship, time was measured by using a half-hour sandglass. Each time the sandglass emptied, the ship’s bell was rung and the sandglass was turned. The day was split into periods called watches. Most watches were four hours long, but the first and last Dog Watches (late afternoon and early evening) were only two hours long. The number of times the bell was rung told the crew what time of day it was. Half an hour into a watch, the bell was rung once. After an hour it was rung twice. After an hour and a half it was rung three times. The end of a four-hour watch was marked by eight bells.
Sandglasses were vital on the Mary Rose for telling the time, and evidence of four (and perhaps a fifth) have been found. When the ship left port, the sandglass would be set running at local noon, which is why the naval day was structured differently to ours today, with a new day starting at noon. A half-hour sandglass was suspended near the helmsman, but the officer of the watch would have a second glass, to prevent the helmsman turning his glass early in order to shorten his shift!
Different sized glasses could measure intervals from as short as half a minute to two hours. A 30-second sandglass, for example, was used by the navigator to time the log reel playing out and measure the ship’s speed using the knots which were spaced every 6 feet on the rope – which is why the speed of ships is still measured in knots!
The bronze ship’s bell was found near the sterncastle, close to a broken beechwood object that may have been the bell hanger. If you visit the Museum, you can see the bell and hear a recording of the original bell sounding to mark the half hours.
Nine pocket sundials were also recovered from the Mary Rose. They relied on the changing direction of the sun as it crossed the sky during the day. They differ from the garden sundials we know today because, being portable, they included a built-in magnetic compass for correct alignment. The Mary Rose sundials were not particularly accurate; they gave an indication of time to perhaps the nearest hour. They are highly decorative with various symbols and designs visible on the dials. They were made abroad (perhaps in Nuremberg) and may have been brought on board by foreign sailors serving on the ship.
The Mary Rose story provides a wide variety of opportunities for practical maths activities for schools, home educators or just for fun! Our ‘Telling the Time’ activity, developed by volunteer Mike Wyles for primary-age children, practises basic maths skills in an imaginative context.
Download the quiz (PDF, 152kb)
